1. Field of the Invention
The present invention pertains to loading bulk material, such as ore, onto troughed belt conveyors. More particularly, the present invention pertains to loading bulk material onto such belt conveyors close to the tail end of the conveyor belt in the region/zone where the belt transitions from flat to troughed.
2. General Background
Bulk material belt conveyors are widely used to move bulk material, including material such as ore, grain, and bulk solid chemicals. Such bulk material belt conveyors each comprise an endless conveyor belt that extends between a tail pulley and a head pulley. Idlers are typically provided in a spaced apart manner between the tail and head pulleys and beneath the upper run of the belt for supporting the weight of the belt and the material thereon. It is common for idlers to include a horizontal center roller(s) or slider bar(s) and opposite tilted wing roller(s) or slider bar(s) to provide the conveyor belt with a trough shaped transverse cross-section. Often, the wing rollers or bars are oriented at thirty-five degrees from horizontal. By providing the conveyor belt with a trough shaped cross-section, more bulk material can be loaded onto the belt without spillage. As should be appreciated, the tail and head pulleys must be cylindrical or nearly cylindrical since the conveyor belt must loop around such pulleys. Thus, the cross-sections of such conveyor belts transition from being generally trough shaped to being generally flat near the pulleys. The transition distance is almost universally calculated based on DIN 22101 (Deutsches Institut Fur Normung E.V., German National Standard), which limits the edge stress of the belt as it goes from flat to troughed. This transition length is customarily limited to no more than 8.5 for fabric and 11.0 for steel cable belts times the vertical rise. The best practice for bulk material conveyor belts is to load a conveyor with material near the tail pulley but where the belt is fully troughed downstream of the transition zone since the cross-section of the belt throughout the transition zone is non-uniform.
In particular situations, such as when space is limited or cost is an issue, it is common (but poor) practice to load a belt conveyor on the transition as close to the tail pulley as possible. However, the edge portions of conveyor belts are generally helical shaped in the transition zone, which makes it difficult to seal a loading chute against the belt in the transition zone and almost always results in skirtboard, wearliner and skirt seal wear, and belt damage. Another way to load a conveyor belt closer to the tail pulley is to lower the angle of the wing roller(s) or bars to thereby decrease the belt edge vertical rise and reduce the acceptable transition distance according to the DIN 22101 design method. However, a lower trough angle has a lower carrying capacity. Yet another technique is to partially trough the belt by raising the terminal pulley above the level of the center roller in an idler set. However, doing that can cause belt buckling and/or cause belts to rise off of idlers.